As a method of implementing gradation drawing having a change in the lights and shades of identical colors and a change in the lights and shades of different colors on a display, there is a method of providing a base line used as a reference for gradation drawing and converting the distance between each pixel and the base line into a color (for example, refer to patent reference 1). Further, as another method, there is a method of implementing gradation drawing by using an alpha blend function which is supported by two-dimensional drawing hardware (for example, refer to patent reference 2). A gradation drawing device described in patent reference 2 generates a three-dimensional model according to a gradation shape expected, and sets a depth after rendering of the three-dimensional model to an alpha value.